/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.reflect;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.truth.Truth.assertThat;
import static com.google.common.truth.Truth.assertWithMessage;

import com.google.errorprone.annotations.RequiredModifiers;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.Comparator;
import javax.lang.model.element.Modifier;

/**
 * Tester of subtyping relationships between two types.
 *
 * <p>Tests should inherit from this class, and declare subtyping relationship with public methods
 * annotated by {@link TestSubtype}.
 *
 * <p>These declaration methods rely on Java static type checking to make sure what we want to
 * assert as subtypes are really subtypes according to javac. For example:
 *
 * <pre>{@code
 * class MySubtypeTests extends SubtypeTester {
 *   @TestSubtype(suppressGetSubtype = true, suppressGetSupertype = true)
 *   public <T> Iterable<? extends T> listIsSubtypeOfIterable(List<T> list) {
 *     return isSubtype(list);
 *   }
 *
 *   @TestSubtype
 *   public List<String> intListIsNotSubtypeOfStringList(List<Integer> intList) {
 *     return notSubtype(intList);
 *   }
 * }
 *
 * public void testMySubtypes() throws Exception {
 *   new MySubtypeTests().testAllDeclarations();
 * }
 * }</pre>
 * <p>
 * The calls to {@link #isSubtype} and {@link #notSubtype} tells the framework what assertions need
 * to be made.
 *
 * <p>The declaration methods must be public.
 */
@AndroidIncompatible // only used by android incompatible tests.
abstract class SubtypeTester implements Cloneable
{

    /**
     * Annotates a public method that declares subtype assertion.
     */
    @RequiredModifiers(Modifier.PUBLIC)
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.METHOD)
    @interface TestSubtype
    {
        /**
         * Suppresses the assertion on {@link TypeToken#getSubtype}.
         */
        boolean suppressGetSubtype() default false;

        /**
         * Suppresses the assertion on {@link TypeToken#getSupertype}.
         */
        boolean suppressGetSupertype() default false;
    }

    private Method method = null;

    /**
     * Call this in a {@link TestSubtype} public method asserting subtype relationship.
     */
    final <T> T isSubtype(T sub)
    {
        Type returnType = method.getGenericReturnType();
        Type paramType = getOnlyParameterType();
        TestSubtype spec = method.getAnnotation(TestSubtype.class);
        assertWithMessage("%s is subtype of %s", paramType, returnType)
                .that(TypeToken.of(paramType).isSubtypeOf(returnType))
                .isTrue();
        assertWithMessage("%s is supertype of %s", returnType, paramType)
                .that(TypeToken.of(returnType).isSupertypeOf(paramType))
                .isTrue();
        if (!spec.suppressGetSubtype())
        {
            assertThat(getSubtype(returnType, TypeToken.of(paramType).getRawType())).isEqualTo(paramType);
        }
        if (!spec.suppressGetSupertype())
        {
            assertThat(getSupertype(paramType, TypeToken.of(returnType).getRawType()))
                    .isEqualTo(returnType);
        }
        return sub;
    }

    /**
     * Call this in a {@link TestSubtype} public method asserting that subtype relationship does not
     * hold.
     */
    final <X> X notSubtype(@SuppressWarnings("unused") Object sub)
    {
        Type returnType = method.getGenericReturnType();
        Type paramType = getOnlyParameterType();
        TestSubtype spec = method.getAnnotation(TestSubtype.class);
        assertWithMessage("%s is subtype of %s", paramType, returnType)
                .that(TypeToken.of(paramType).isSubtypeOf(returnType))
                .isFalse();
        assertWithMessage("%s is supertype of %s", returnType, paramType)
                .that(TypeToken.of(returnType).isSupertypeOf(paramType))
                .isFalse();
        if (!spec.suppressGetSubtype())
        {
            try
            {
                assertThat(getSubtype(returnType, TypeToken.of(paramType).getRawType()))
                        .isNotEqualTo(paramType);
            }
            catch (IllegalArgumentException notSubtype1)
            {
                // The raw class isn't even a subclass.
            }
        }
        if (!spec.suppressGetSupertype())
        {
            try
            {
                assertThat(getSupertype(paramType, TypeToken.of(returnType).getRawType()))
                        .isNotEqualTo(returnType);
            }
            catch (IllegalArgumentException notSubtype2)
            {
                // The raw class isn't even a subclass.
            }
        }
        return null;
    }

    final void testAllDeclarations() throws Exception
    {
        checkState(method == null);
        Method[] methods = getClass().getMethods();
        Arrays.sort(
                methods,
                new Comparator<Method>()
                {
                    @Override
                    public int compare(Method a, Method b)
                    {
                        return a.getName().compareTo(b.getName());
                    }
                });
        for (Method method : methods)
        {
            if (method.isAnnotationPresent(TestSubtype.class))
            {
                method.setAccessible(true);
                SubtypeTester tester = (SubtypeTester) clone();
                tester.method = method;
                method.invoke(tester, new Object[]{null});
            }
        }
    }

    private Type getOnlyParameterType()
    {
        assertThat(method.getGenericParameterTypes()).hasLength(1);
        return method.getGenericParameterTypes()[0];
    }

    @SuppressWarnings({"rawtypes", "unchecked"})
    private static Type getSupertype(Type type, Class<?> superclass)
    {
        Class rawType = superclass;
        return TypeToken.of(type).getSupertype(rawType).getType();
    }

    private static Type getSubtype(Type type, Class<?> subclass)
    {
        return TypeToken.of(type).getSubtype(subclass).getType();
    }
}
